The story of Baldur's Gate that started with BG1 ends in BG3, so there will likely not ever be a BG4. If they make another Baldur's Gate game it will be something else entirely...a whole new story. I suspect that Larian will make more D&D games but I don't think their next D&D game will be a Baldur's Gate game.
DOS3 may happen next as well, Larian have said they aren't done with the Divinity games, but they do have a team of 400 developers now so they can probably split that team to work on two games at once...put something like 100 on the next Divinity game and 300 on the next D&D game...that might work.
There absolutely will be another Baldur’s Gate game at some point. Even if the story is completely disconnected, the name is now a more potent brand than ever. The Baldur’s Gate 3: The Black Hound that BioWare was making was a completely new story. Still kept the name. Baldur’s Gate 2 doesn’t even take place in the eponymous city. Brand name recognition is important.
